Transcription and Translation Practice

Transcription (copying DNA code) is going from DNA to RNA.  DNA is too big to exit the nucleus, but RNA is not.  In order for the code to get out of the nucleus, it needs to be copied into RNA.  RNA has the bases A, C, and G, but not T.  instead of Thymine, it has Uracil or U.  As with DNA replication, C bond to G, but A now bind to U.  Again DNA is opened by helicase, but this time RNA polymerase binds and copies the DNA to create a single stranded RNA complimentary strand.  The DNA then coils back to its original form after RNA polymerase has left.  This strand is called mRNA or messenger RNA.

Original DNA Strand:

AATTCATCCGTAATC

mRNA strand:

UUAAGUAGGCAUUAG (same as DNA replication, but now there is a U instead of T)

mRNA leaves the nucleus and travels to the ribosome (also called rRNA – ribosomal RNA).  Ribosomes make proteins so this is where the code of DNA is used to form a protein.  mRNA binds to rRNA.  As rRNA reads the code a third RNA, tRNA (transfer RNA) brings in the correct amino acid and will then combine to form a protein.  (A protein is a chain of amino acids). 

The tRNA looks like a T shape and has the complimentary code to the mRNA on one end (called an anticodon)  and the amino acid that represents the mRNA codon on the other end. 

KEY NOTE:

DNA is read in a three letter sequence called codons.  I like to divide my DNA up into codons from the beginning so that it is easier to copy the sequence without mistakes. 

From DNA example above – broken into codons:

Original DNA Strand:

AAT/TCA/TCC/GTA/ATC

mRNA strand:

UUA/AGU/AGG/CAU/UAG

tRNA anticodon (bonds with mRNA):

AAU/UCA/UCC/GUA/AUC

tRNA has the anticodon to the mRNA strand.  It is identical to the original DNA with the exception of Uracil replaced Thymine.  The anticodon bonds to the codon of the mRNA.

The last step is to figure out the amino acid sequence (read in codons from the mRNA strand).  In order to do this, you need to use the amino acid chart.  Find the first letter in the column on the left.  Go to the second letter on the column along the top.  Finally find the third letter in the column on the right.  One amino acid can be coded for with several RNA sequences. 

From the above example:

mRNA stand:

UUA/AGU/AGG/CAU/UAG

Amino acid sequence:

Leu-Ser-Arg-His-Stop

You will notice in the chart some of the sequences code for a start and some for a stop.  The ribosome won’t start making the protein until it reads a start codon.  They will then code until they read a stop codon. 

Now you try the following problems.  Remember to separate your amino acids with a dash.  This was a quiz put into canvas.  2 points each for a total of 12 points with two bonus